The present invention relates to a data compression control device and, more particularly, to a data compression control device in a data recording system for recording compressed data on a recording medium such as a magnetic tape.
As a device for recording compressed data at a constant rate on a recording medium such as a magnetic tape, there is known a data compressing circuit which is disclosed in Japanese Patent Laid-Open No. 58-102314, for example. This circuit performs data compression at a high rate by means of hardware. According to this technique, the number of bytes of the compressed data may increase to an amount which is more than that of the data before the compression. With this circuit, therefore, the number of bytes of the compressed data and the number of bytes of the uncompressed data are compared so that the data having fewer bytes is written on the recording medium. After all the data transferred has been compressed, however, the number of bytes before and after compression is compared, and data is then written on the recording medium. This makes it necessary to provide a data buffer having a capacity sufficient to store all the compressed data temporarily in the buffer. Moreover, there arises a problem that a delay occurs in the data processing period after the data has been transferred from a CPU, written on the recording medium and confirmed to be correct and before the CPU and the recording system are disconnected.
When the compressed data is written on the recording medium at a constant rate before completion of data transfer from the CPU, a defect results in that the data to be written on the recording medium is exhausted causing an overrun error when the coefficient of compression is extremely high.